This application claims the priority of German Application No. 199 19 688.5 filed Apr. 30, 1999, which is incorporated herein by reference.
The invention relates to a method of coating an inner surface of a weapon barrel with at least one layer for protecting the inner barrel surface against corrosion.
Because of the significantly augmented performance of present-day ammunition, substantial corrosion phenomena appear particularly in weapon barrels made of steel, due to the high gas temperatures and flow velocities occurring when the weapon is fired. Such corrosion results in a worn weapon barrel before it reaches the period when material fatigue sets in. It has been known to provide the weapon barrels with a hard chromium layer to avoid such corrosion. In the conventional processes the hard chromium is deposited electrolytically on the inner surface of the weapon barrel.
It is, among others, a disadvantage of the known processes that the electrolytically deposited hard chromium layers do not adequately resist the effects of performance-enhanced ammunition. As a result, the chromium layer tends to peel and thus significant corrosions appear on the exposed inner surface portions.
German Offenlegungsschrift (application published without examination) 195 44 824 and German Patent No. 197 41 028 disclose methods for hardening weapon barrels by means of a laser beam. The laser beam is axially introduced into the weapon barrel and is caused to impinge on the inner face of the barrel by means of a beam deflecting optical assembly which is displaceable within the weapon barrel.
It is an object of the invention to provide an improved method for the internal coating of a weapon barrel by means of which, for avoiding corrosions, coating materials of high melting point may be applied with a high degree of adhesion to the inner barrel surface of the weapon.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the method of coating an inner surface of a weapon barrel includes the following steps: directing a laser beam against the inner barrel surface to cause melting of regions thereof; introducing a coating material in one of powder, wire and ribbon form into the laser beam for melting the coating material to produce in the surface regions a molten bath composed of the molten coating material and a material of the weapon barrel; and moving the laser beam inside the weapon barrel axially thereof and relative thereto, whereby the molten substance of the bath becomes rigid as the laser beam moves away therefrom.
It is thus the basic principle of the invention to perform an inner coating of the weapon barrel by laser welding by directing on the inner surface of the weapon barrel a laser beam which melts the upper inner surface region of the weapon barrel. The coating material is introduced in powder, wire or ribbon form briefly before the impingement of the laser beam on the inner barrel face and is melted by the laser beam so that in the surface regions of the weapon barrel a molten bath is formed by the molten barrel material and the coating substance which becomes rigid as the laser beam travels further.
By a suitable relative motion between the laser beam and the weapon barrel a surface coating of the inner surface of the weapon barrel may be obtained. Further, by repeating the coating process it is possible to sequentially provide different layers and to adapt the weapon barrel to the respective requirements.
It is a significant advantage of the method according to the invention that high-melting point substances such as niobium, molybdenum, tantalum, hafnium, vanadium, tungsten, zirconium or alloys thereof may be applied in layer thicknesses up to a few millimeters on the inner surface of the weapon barrel. It is noted in this connection that substances such as molybdenum or tantalum cannot be separated from aqueous electrolytes with the known galvanic processes. Further, with the known processes layer thicknesses of only a few tenths of a millimeter may be produced.
The coating may be performed on the entire inner surface of the weapon barrel or on selective length portions thereof. In either case, care has to be taken to adapt the weapon barrel to the intended thickness of the coating before the coating process, that is, the barrel portion to be coated has to have a diameter which corresponds to the weapon caliber plus twice the thickness of the coating.
For performing a coating of the weapon barrel with high-melting point metal salts, such as carbides or nitrides, it has been found advantageous to introduce into the plasma a suitable gas in addition to the metal, for example, methane for forming carbides or nitrogen for forming nitrides.